Method for forming ink droplets in ink-jet type printer and ink-jet type recording device

Abstract

An ink-jet type recording device and a method for generating ink droplets in such a recording device in which a time difference between the leading and trailing ends of an ink column jetted out from a nozzle opening is reduced without decreasing the average speed of the ink column so as to prevent generation of satellites droplets and the like. A capacitor maintaining a voltage for expansion of a pressure generation chamber is discharged by switching a plurality of resistances differing in the discharge resistance thereof by means of switching transistors. As a result, the terminal voltage of the capacitor is caused to vary at a speed which is determined by the values of the resistances. Therefore, by selecting the values of the resistances such that the absolute value of the differential value of the terminal voltage increases with time, the rate of contraction of the pressure generation chamber can be increased gradually to thereby minimize a speed difference between the leading and trailing ends of the ink column.

What is claimed is: 
     
       1. An ink droplet forming method for driving an ink-jet type recording head including a pressure generation chamber which receives ink supplied from a reservoir, a flow passage forming member associated with said pressure generation chamber and having a nozzle opening, and a piezoelectric vibrator associated with said pressure generation chamber for varying a volume of said pressure generation chamber to jet ink droplets from said pressure generation chamber through said nozzle opening in said flow passage forming chamber, said method comprising the steps of: expanding said pressure generation chamber to thereby suck ink into said pressure generation chamber;   contracting said pressure generation chamber at a first speed during a first time period to commence jetting of an ink droplet through said nozzle, said first speed being constant during said first time period; and   contracting said pressure generation chamber at a second speed during a second time period different from said first speed while said ink droplet continues to be jetted through said nozzle, said second speed being constant during said second time period and greater than said first speed, said second time period being immediately subsequent to said first time period.   
     
     
       2. An ink droplet forming method for driving an ink-jet type recording head including a pressure generation chamber which receives ink supplied from a reservoir, a flow passage forming member associated with said pressure generation chamber and having a nozzle opening, and a piezoelectric vibrator associated with said pressure generation chamber for varying a volume of said pressure generation chamber to jet ink droplets from said pressure generation chamber through said nozzle opening in said flow passage forming member, said method comprising the steps of: contracting said pressure generation chamber at a first speed during a first time period to commence jetting of an ink droplet through said nozzle, said first speed being constant during said first time period;   contracting said pressure generation chamber at a second speed during a second time period different from said first speed while said ink droplet continues to be jetted through said nozzle, said second speed being constant during said second time period and greater than said first speed, said second time period being immediately subsequent to said first time period; and   expanding said pressure generation chamber to thereby suck ink into said pressure generation chamber.   
     
     
       3. An ink-jet type recording device comprising: an ink-jet type recording head including a pressure chamber which receives ink supplied from a reservoir;   a flow passage forming member associated with said pressure generation chamber and having a nozzle opening;   a piezoelectric vibrator associated with said pressure generation chamber for varying a volume of said pressure generation chamber to jet ink droplets from said pressure generation chamber through said nozzle opening in said flow passage forming member; and   a drive circuit for producing a first drive signal in response to a timing signal, said first drive signal being applied to said piezoelectric vibrator to expand said pressure generation chamber to thereby suck ink into said pressure generation chamber, and, after completion of expansion of said pressure generation chamber, for producing a second drive signal including at least two parts one after another whose differential functions are constants, which are applied to said pressure generation chamber to cause said pressure generation chamber to contract, said constants having different absolute values, said absolute values increasing with time.   
     
     
       4. The ink-jet type recording device as set forth in claim 3, wherein said drive circuit further produces a hold signal having a voltage which is held constant for a predetermined period of time between said first and second drive signals. 
     
     
       5. The ink-jet type recording device as set forth in claim 3, wherein said drive circuit comprises first switching means which is turned on in accordance with said timing signal to thereby charge a capacitor, and a plurality of second switching means which are turned on one by one after completion of charging of said capacitor to thereby discharge said capacitor with different constant current values. 
     
     
       6. An ink-jet type recording device comprising: an ink-jet type recording head including a pressure chamber which receives ink supplied from a reservoir;   a flow passage forming member associated with said pressure generation chamber and having a nozzle opening;   a piezoelectric vibrator associated with said pressure generation chamber for varying a volume of said pressure generation chamber to jet ink droplets from said pressure generation chamber through said nozzle opening in said flow passage forming member; and   a drive circuit for outputting a first drive signal including at least two voltage signals one after another whose differential functions are constants in response to timing signals, said pressure generation chamber contracting in response to said voltage signals, said constants having different absolute values from each other, said absolute values increasing with time and, after completion of said first drive signal, for outputting a second drive signal, said pressure generation chamber expanding in response to said second drive signal.   
     
     
       7. The ink-jet type recording device as set forth in claim 6, wherein said drive circuit further produces a hold signal having a voltage which is held constant for a predetermined period of time between said first and second drive signals. 
     
     
       8. The ink-jet type recording device as set forth in claim 6, wherein said drive circuit comprises first switching means which is turned on one by one in accordance with said timing signal to thereby charge a capacitor, and a plurality of second switching means which are turned on after completion of charging of said capacitor to thereby discharge said capacitor with different constant current values.